JP6002016B2 - Capacitive pressure sensor - Google Patents

Description

  The present invention relates to a capacitance type pressure sensor including a pressure sensor chip having a diaphragm structure for detecting capacitance according to the pressure of a medium to be measured.

  2. Description of the Related Art Conventionally, diaphragm type pressure sensors that detect changes in measured pressure as changes in capacitance are widely known. As an example of this pressure sensor, by covering a communication hole between the vacuum chamber and the diaphragm vacuum gauge, it is possible to prevent unreacted products, side reaction products and particles from entering the vacuum gauge from the vacuum chamber, A capacitance-type pressure sensor is known that prevents deposition components such as products and particles from adhering to the diaphragm and depositing them (see, for example, Patent Document 1).

  In the capacitance-type pressure sensor disclosed in Patent Document 1, it is possible to reduce adhesion of a deposition component having a high degree of straightness contained in a medium to be measured to the diaphragm. However, because the pressure of the medium to be measured needs to be guided to the diaphragm, it is impossible to completely remove the deposited components by the filter.

  When a part of the deposition component in the medium to be measured adheres to the diaphragm and deposits, the diaphragm is bent in one direction, and a zero point shift (zero point movement) occurs. That is, the deposit attached to the diaphragm generates an internal stress such as a compressive stress or a tensile stress depending on its component. As the stress is generated, the diaphragm surface on the side in contact with the medium to be measured is pulled or compressed, and the balance of force in the thickness direction of the diaphragm is lost. Thus, the diaphragm bends so that the measured medium side is convex or the opposite side of the measured medium is convex.

  Since it is impossible to always match different deposits and diaphragm materials for each medium to be measured, and it is rare that the atomic arrangement of the deposits and diaphragms match microscopically completely. As described above, the deposit adhering to the film causes contraction or elongation. And the deflection of a diaphragm becomes so large that the deposit which adheres to a diaphragm increases.

  The electrostatic capacity type pressure sensor detects a pressure difference based on the electrostatic capacity that changes due to the deflection of the diaphragm. If the diaphragm bends due to deposits adhering to the diaphragm, even if there is no pressure difference between the two sides of the diaphragm, a signal indicating that there is a pressure difference will be detected, so that a zero error called a so-called zero shift will occur. Thus, an error occurs in the pressure measurement. In order to avoid this pressure measurement error, it is necessary to frequently replace the capacitance type pressure sensor, which causes a problem that the cost increases.

  Therefore, the thickness of the central part of the diaphragm is made thinner than the peripheral part, and the rigidity of the central part is made lower than that of the peripheral part, thereby suppressing the bending of the diaphragm due to the internal stress of the deposit. A capacitive pressure sensor has been proposed (see, for example, Patent Document 2).

JP-A-10-153510 JP 2010-236949 A

  The capacitance-type pressure sensor disclosed in Patent Document 2 is based on the premise that a homogeneous film is formed on the diaphragm by deposits. However, in reality, deposition of a film on the diaphragm is unavoidable, and in fact, the film thickness distribution in which the film thickness distribution is biased depending on the process material, process conditions, vacuum gauge structure, vacuum gauge position, etc. In that case, the above assumption is not satisfied. In the following, ALD (Atomic Layer Deposition) is taken as a specific example to infer the principle of ALD and the reason why the film thickness distribution is biased.

The capacitive pressure sensor is installed in a chamber used in a semiconductor manufacturing process, for example, and is used as a vacuum gauge. In this semiconductor manufacturing process, ALD (Atomic Layer Deposition), which is mainly used for forming an insulating film, is a film forming method premised on a surface adsorption reaction, and is called a precursor gas containing an element of the film to be formed. A film is formed by alternately reacting the surface of a material gas and a reactive gas (in many cases, an oxidizing gas). For example, when depositing AlO, the precursor gas is trimethylaluminum, and the reaction gas (oxidant gas) is H ₂ O, O ₃ or the like.

Specifically, ALD repeats the following cycles (A) to (D).
(A) A precursor gas is introduced into the chamber and adsorbed on the wafer surface.
(B) The precursor gas other than the monoatomic layer on the wafer surface is purged (removed) by evacuating the chamber or introducing an inert gas into the chamber.
(C) A reaction gas is introduced into the chamber and reacted with the precursor gas.
(D) Purge the reaction product and excess reaction gas by evacuating the chamber or introducing an inert gas into the chamber.
As described above, since ALD is performed at the atomic level by the adsorption of the material gas on the wafer surface and the chemical reaction between the adsorbed material gas and the reactive gas, a via hole having a large aspect ratio on the wafer or complicated It is characterized in that a film can be uniformly formed on a portion having a three-dimensional structure. However, on the other hand, film formation is performed not only on the wafer but also in every part of the process chamber including the vacuum gauge, which often causes the problems described above.

Next, the reason why an ALD that forms a uniform film in principle and a partially non-uniform film is formed will be described. In the film formation on the ALD process wafer, if the purge is not performed sufficiently, the remaining gas will be mixed in the chamber and a gas phase reaction will occur instead of a surface reaction, resulting in undesirable reaction product particles. It is known that the film cannot be formed well.
A vacuum gauge is usually installed in a peripheral portion of a chamber where a wafer to be processed is placed, which is not a wafer placement location, and in many cases, a gas in the chamber is guided to a diaphragm via a pipe. Yes. For this reason, it is assumed that the gas replacement property near the diaphragm is worse than that on the wafer. Furthermore, due to the structure in the vicinity of the diaphragm, if a region with poor gas conductance (easiness to pass) is partially present on the diaphragm, the gas replacement property is poor in that region, so that the film cannot be formed well and the conductance is good. The film deposited on the diaphragm is expected to be thinner than the area. As described above, in principle, film deposition on the diaphragm is unavoidable in ALD, and the film thickness distribution on the diaphragm is biased depending on the process material, process conditions, vacuum gauge structure, vacuum gauge position, etc. It is possible to get out.

  The capacitance type pressure sensor disclosed in Patent Document 2 is based on the premise that the thickness of the film deposited on the diaphragm is uniform. Therefore, if the film thickness distribution on the diaphragm is uneven, the deflection of the diaphragm It becomes impossible to suppress the zero shift. In particular, if the conductance of the gas at the center of the diaphragm where the electrode for pressure detection is located is good and the conductance of the gas at the outer periphery of the diaphragm is poor, the film deposited on the center of the diaphragm becomes thick, and a large moment due to film stress As a result, a large zero shift occurs.

  The present invention has been made to solve the above-described problems, and suppresses zero shift even when a capacitive pressure sensor is applied to an apparatus using a film forming method in which the film thickness distribution on the diaphragm is biased. It is an object of the present invention to provide a capacitive pressure sensor that can be used.

The capacitance type pressure sensor of the present invention includes a diaphragm whose central portion is displaced according to the pressure of the medium to be measured, a sensor base that fixes a peripheral portion of the diaphragm and forms a reference vacuum chamber together with the diaphragm, A cover plate that is joined to a peripheral portion of the diaphragm on the side opposite to the sensor base and forms a pressure introducing chamber together with the diaphragm, a fixed electrode formed on the surface of the sensor base on the reference vacuum chamber side, and the fixed electrode And a movable electrode formed on a surface of the diaphragm on the reference vacuum chamber side so as to face each other, and the cover plate is a pressure for introducing the medium to be measured into the pressure introducing chamber from a direction intersecting the surface of the diaphragm It has a penetrating hole, a plurality of the pressure introducing hole, substantially symmetrical with respect to the center of the diaphragm at a position on the circumference surrounding the center of the diaphragm Are arranged so as to be positioned in a range from the center of the 50.0% 70.0% along the surface direction of the diaphragm of the diaphragm when the radius of the diaphragm is 100%, the plurality of pressure introducing A hole is arranged.
In one configuration example of the capacitive pressure sensor of the present invention, the movable electrode includes a pressure-sensitive movable electrode formed so that the center thereof coincides with the center of the diaphragm, and an outer side of the pressure-sensitive movable electrode. A reference-side movable electrode formed on the pressure-side movable electrode, the pressure-sensitive side fixed electrode formed to face the pressure-sensitive side movable electrode, and a reference formed to face the reference-side movable electrode. It consists of a side fixed electrode.

  According to the present invention, by arranging the pressure introduction hole so as to be located in the range of 50.0% to 70.0% from the center of the diaphragm along the surface direction of the diaphragm, Capacitance-type pressure sensor in a device that uses a film forming method that can relax the moment due to the increased film stress due to the poor balance of the film thickness and that causes a bias in the film thickness distribution on the diaphragm, such as ALD Even when this is applied, the zero shift can be suppressed.

It is sectional drawing which shows the structure of the electrostatic capacitance type pressure sensor which concerns on embodiment of this invention. It is a top view which shows arrangement | positioning of the pressure-sensitive side fixed electrode and reference side fixed electrode which were formed in the sensor base. It is a figure explaining operation | movement of the electrostatic capacitance type pressure sensor which concerns on embodiment of this invention. It is a figure which shows the relationship between the position of a pressure introduction hole, and the shift rate of a sensor output. It is sectional drawing which shows the structure of the conventional electrostatic capacitance type pressure sensor. It is a top view which shows the example of arrangement | positioning of the pressure introduction hole in embodiment of this invention. It is a top view which shows another example of arrangement | positioning of the pressure introduction hole in embodiment of this invention.

[Principle of the Invention]
The inventor strongly generates a bending moment that causes the diaphragm to bend due to the film stress in the thickly formed part on the diaphragm of the capacitive pressure sensor. Therefore, if the conductance of the gas in the space on the diaphragm is controlled, It was conceived that the film thickness distribution on the diaphragm can be controlled and the deflection of the diaphragm, that is, the zero point shift can be controlled. Specifically, the opening of the capacitive pressure sensor that guides the pressure of the medium to be measured is formed outside the center of the diaphragm. More specifically, a plurality of small openings having the same total opening area as this opening instead of one opening formed at the center position of the diaphragm in the conventional capacitive pressure sensor. Is possible to arrange them at positions on the circumference surrounding the center of the diaphragm.

[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of a capacitive pressure sensor according to an embodiment of the present invention. The capacitance-type pressure sensor includes a cover plate 1 made of sapphire, which is a single crystal of aluminum oxide, and a pressure sensor chip 2 joined to the cover plate 1. The pressure sensor chip 2 includes a sensor base 20 made of sapphire, a diaphragm 21 made of sapphire joined to the sensor base 20, a spacer 22 made of sapphire joined to the diaphragm 21, platinum formed on the sensor base 20, and the like. Pressure-sensitive side fixed electrode 23 made of a conductive material, a reference-side fixed electrode 24 made of a conductor such as platinum formed on the sensor pedestal 20, and platinum formed on the diaphragm 21 so as to face the pressure-sensitive side fixed electrode 23. A pressure-sensitive movable electrode 25 made of a conductor and a reference-side movable electrode 26 made of a conductor such as platinum formed on the diaphragm 21 so as to face the reference-side fixed electrode 24 are configured.

  By providing a spacer 22 in which a through hole 22 a having a substantially circular shape in plan view is formed between the cover plate 1 and the diaphragm 21, a space having a substantially circular shape in plan view (hereinafter referred to as pressure) is provided between the cover plate 1 and the diaphragm 21. 27) is formed. Further, by providing a concave portion 21a having a substantially circular shape in plan view on the surface of the diaphragm 21 on the sensor pedestal 20 side, a substantially circular vacuum space (hereinafter referred to as a reference vacuum chamber) between the sensor pedestal 20 and the diaphragm 21 is provided. 28) is formed.

  The sensor base 20 and the diaphragm 21 are joined via an aluminum oxide-based joining material that changes to sapphire after joining. Similarly, the diaphragm 21 and the spacer 22 are joined via an aluminum oxide-based joining material. Since such a joining method is described in detail in Japanese Patent Laid-Open No. 2002-111101, detailed description thereof is omitted. Note that the spacer 22 may be eliminated by forming a spacer-like protrusion at the lower portion of the cover plate 1.

  FIG. 2 is a plan view showing the arrangement of the pressure-sensitive fixed electrode 23 and the reference-side fixed electrode 24 formed on the sensor base 20. The pressure-sensitive side fixed electrode 23 having a substantially circular shape in plan view is formed on the surface of the sensor base 20 on the reference vacuum chamber 28 side so that the center thereof substantially coincides with the center of the diaphragm 21. The reference-side fixed electrode 24 having a substantially arc shape in plan view is formed on the surface of the sensor base 20 on the reference vacuum chamber 28 side so as to be disposed substantially concentrically outside the pressure-sensitive side fixed electrode 23. The pressure-sensitive side fixed electrode 23 is electrically connected to a signal processing device (not shown) outside the sensor via a wiring 29 formed on the sensor base 20. Similarly, the reference side fixed electrode 24 is electrically connected to the signal processing device via the wiring 30 formed on the sensor base 20.

  The configuration of the movable electrode on the diaphragm 21 side is the same as that of the fixed electrode. That is, the pressure-sensitive movable electrode 25 having a substantially circular shape in plan view is formed on the surface of the diaphragm 21 on the reference vacuum chamber 28 side so as to face the pressure-sensitive fixed electrode 23. The center of the pressure-sensitive movable electrode 25 substantially coincides with the center of the diaphragm 21. The reference-side movable electrode 26 having a substantially arc shape in plan view is formed on the surface of the diaphragm 21 on the standard vacuum chamber 28 side so as to face the reference-side fixed electrode 24. The reference side movable electrode 26 is disposed substantially concentrically outside the pressure sensitive side movable electrode 25. The pressure-sensitive movable electrode 25 is electrically connected to a signal processing device outside the sensor via wiring (not shown) formed on the diaphragm 21. Similarly, the reference-side movable electrode 26 is electrically connected to the signal processing device via wiring (not shown) formed on the diaphragm 21.

  The pressure-sensitive side fixed electrode 23 and the pressure-sensitive side movable electrode 25 are highly sensitive to pressure and serve to perform pressure measurement. The reference-side fixed electrode 24 and the reference-side movable electrode 26 are low in sensitivity to pressure and play a role of correcting the dielectric constant between the electrodes.

  The cover plate 1 joined to the pressure sensor chip 2 as described above is provided with a pressure introduction hole 10 formed so as to penetrate the cover plate 1 in order to guide the medium to be measured to the pressure introduction chamber 27. . Details of the pressure introducing hole 10 will be described later. The cover plate 1 and the spacer 22 of the pressure sensor chip 2 are bonded via an aluminum oxide-based bonding material that changes to sapphire after bonding.

  Next, the operation of the capacitive pressure sensor of this embodiment will be described. FIG. 3 is a diagram for explaining the operation of the capacitive pressure sensor. When the medium to be measured is introduced into the pressure introducing chamber 27 through the pressure introducing hole 10 from the direction intersecting the surface of the diaphragm 21 (direction perpendicular to the surface of the diaphragm 21 in the examples of FIGS. 1 and 3), FIG. As shown in FIG. 3, the diaphragm 21 is deformed in accordance with the pressure of the medium to be measured. When the capacitive pressure sensor is used as a vacuum gauge in a semiconductor manufacturing process, the medium to be measured is a gas inside the chamber.

When the diaphragm 21 is deformed, the distance between the sensor pedestal 20 and the diaphragm 21 (the height of the reference vacuum chamber 28) changes, the capacitance between the pressure-sensitive side fixed electrode 23 and the pressure-sensitive side movable electrode 25, and the reference-side fixed electrode 24. And the reference side movable electrode 26 change. Assuming that the capacitance between the pressure-sensitive side fixed electrode 23 and the pressure-sensitive side movable electrode 25 is Cx and the capacitance between the reference-side fixed electrode 24 and the reference-side movable electrode 26 is Cr, the sensor output K is calculated as follows: Is done.
K = (Cx−Cr) / Cx (1)
A signal processing device (not shown) can measure the pressure of the medium to be measured by calculating the sensor output K according to the equation (1) and converting the sensor output K (capacitance value) into a pressure value.

  Next, the pressure introducing hole 10 of the cover plate 1 will be described. In the present embodiment, in order to control the conductance of the medium to be measured in the pressure introduction chamber 27, a position on the circumference surrounding the center of the diaphragm 21 (the circumference of a circle centering on a point coincident with the center of the diaphragm 21). By disposing a plurality of pressure introduction holes 10 in the upper position), the film thickness distribution of the deposits attached to the diaphragm 21 is controlled. In the example of FIG. 2, the position of the pressure introduction hole 10 formed in the cover plate 1 is indicated by a broken line. In the example of FIG. 2, four pressure introduction holes 10 are arranged.

  FIG. 4 is a diagram showing the relationship between the position of the pressure introducing hole 10 and the shift rate of the sensor output. FIG. 4 shows a pressure in the range of 40.0% to 80.0% from the center of the diaphragm 21 along the surface direction of the diaphragm 21 (direction parallel to the paper surface of FIG. 2) when the diaphragm radius is 100%. The sensor output shift rate when the position of the introduction hole 10 is changed is obtained by simulation. Here, the sensor output shift rate is calculated for the case where four pressure introduction holes 10 are provided on the circumference surrounding the center of the diaphragm 21. As is clear from the fact that the recess 21a and the through hole 22a are substantially circular in plan view, the diaphragm 21 exposed in the pressure introducing chamber 27 and the reference vacuum chamber 28 is substantially circular in plan view. As shown in FIG. 1, the diaphragm radius means a distance R from the center of the diaphragm 21 to the inner wall of the spacer 22. The horizontal axis of FIG. 4 shows the ratio T / Tmax between the film thickness Tmax at the thickest portion of the deposit adhering to the diaphragm 21 and the film thickness T at the surrounding area, with the film thickness Tmax being 100%. is there.

  The sensor output shift rate indicates the shift rate of the sensor output of the capacitive pressure sensor of the present embodiment with respect to the sensor output of the conventional capacitive pressure sensor. Here, FIG. 5 shows a configuration of a conventional capacitive pressure sensor used for comparison. In FIG. 5, the same components as those in FIG. As shown in FIG. 5, in the conventional capacitive pressure sensor, a pressure introduction hole 10 b is formed at the center position of the diaphragm 21. The area of the pressure introducing hole 10b and the total area of the four pressure introducing holes 10 are the same. In the conventional capacitive pressure sensor, the deposit is thickest in the vicinity of the center of the diaphragm 21 immediately below the pressure introducing hole 10b, whereas in the present embodiment, the pressure introducing hole outside the center of the diaphragm 21 is used. The deposit is thickest immediately below 10.

The sensor output of the conventional capacitive pressure sensor when no pressure is applied to the diaphragm 21 is K0, and similarly the sensor output of the capacitive pressure sensor of the present embodiment when no pressure is applied to the diaphragm 21. Is K1, the sensor output shift rate SR is calculated as follows.
SR = (K1-K0) / K0 (2)

When there is uniform deposition on the diaphragm of the conventional capacitive pressure sensor of FIG. 5, the sensor output shift rate SR is 100%.
FIG. 4 shows that the zero point shift is improved with respect to the conventional capacitive pressure sensor when the sensor output shift rate SR is in the range of −100% to 100%. The sensor output shift rate SR falls within the range of −100% to 100% when the center position of the pressure introducing hole 10 is within the range of 50.0% to 70.0% from the center of the diaphragm 21. Therefore, it can be seen that if the center position of each pressure introducing hole 10 is set in the range of 50.0% to 70.0% from the center of the diaphragm 21, the zero point shift can be suppressed.

  The reason why such a numerical range is good is considered to be as follows. In the conventional capacitance type pressure sensor, the deposit becomes thickest near the center of the diaphragm 21, so that the deflection of the diaphragm 21 due to the deposit increases. The influence of this bending cannot be canceled out even if the calculation shown in Expression (1) is performed.

  As a specific method for controlling the film thickness distribution, the center position of the pressure introducing hole 10 may be set at 50.0% from the center O of the diaphragm 21 as shown in FIG. In this method, the distance from the center O of the diaphragm 21 to the pressure introduction hole 10 and the distance from the pressure introduction hole 10 to the end of the diaphragm 21 are equalized. As another control method, as shown in FIG. 7, the center position of the pressure introducing hole 10 may be set at a position of 70.0% from the center O of the diaphragm 21. This method is a method of equalizing the area of the circle 100 inside the pressure introducing hole 10 and the area obtained by subtracting the area of the circle 100 from the area of the diaphragm 21. By such a method, the film thickness distribution on the diaphragm 21 can be made into a theoretically desirable shape.

  Also in the present embodiment, the deposit becomes the thickest directly under the pressure introducing hole 10, but even if there is such a thickness deviation, the influence of the deflection of the diaphragm 21 due to this thickness deviation is as follows. It can be canceled by the calculation shown in equation (1).

  As described above, in the present embodiment, the center of the pressure introduction hole 10 is located within the range of 50.0% to 70.0% from the center of the diaphragm 21, so that the top of the diaphragm is similar to ALD. Even when the capacitance type pressure sensor is applied to an apparatus using a film forming method in which the film thickness distribution is biased, the zero point shift of the capacitance type pressure sensor can be suppressed.

  The present invention can be applied to a capacitive pressure sensor including a pressure sensor chip having a diaphragm structure.

  DESCRIPTION OF SYMBOLS 1 ... Cover plate, 2 ... Pressure sensor chip, 10 ... Pressure introduction hole, 20 ... Sensor base, 21 ... Diaphragm, 21a ... Recessed part, 22 ... Spacer, 22a ... Through-hole, 23 ... Pressure-sensitive side fixed electrode, 24 ... reference Side fixed electrode, 25 ... Pressure-sensitive movable electrode, 26 ... Reference-side movable electrode, 27 ... Pressure introduction chamber, 28 ... Reference vacuum chamber, 29, 30 ... wiring.

Claims (2)

A diaphragm whose central portion is displaced according to the pressure of the medium to be measured;
A sensor base that fixes the peripheral edge of the diaphragm and forms a reference vacuum chamber together with the diaphragm;
A cover plate that is joined to a peripheral portion of the diaphragm opposite to the sensor base and forms a pressure introducing chamber together with the diaphragm;
A fixed electrode formed on the surface of the sensor base on the reference vacuum chamber side;
A movable electrode formed on the surface of the diaphragm on the reference vacuum chamber side so as to face the fixed electrode,
The cover plate has a pressure introduction hole for introducing the medium to be measured into the pressure introduction chamber from a direction intersecting the surface of the diaphragm.
A plurality of the pressure introducing holes are arranged substantially symmetrically with respect to the center of the diaphragm at positions on a circumference surrounding the center of the diaphragm, and the radius of the diaphragm is assumed to be 100% from the center of the diaphragm. The capacitance-type pressure sensor, wherein the plurality of pressure introduction holes are arranged so as to be located in a range of 50.0% to 70.0% along a surface direction of the diaphragm. The capacitive pressure sensor according to claim 1 ,
The movable electrode is composed of a pressure-sensitive movable electrode formed so that its center coincides with the center of the diaphragm, and a reference-side movable electrode formed outside the pressure-sensitive movable electrode,
The stationary electrode includes a pressure-sensitive side fixed electrode formed to face the pressure-sensitive side movable electrode and a reference-side fixed electrode formed to face the reference-side movable electrode. Capacitive pressure sensor.